The present invention relates to a laser device comprising an array of vertical cavity surface emission lasers (VCSELs). Vertical cavity surface emitting laser diodes are one of the most promising laser sources and offer many advantages compared to edge emitters, like addressable 2D-array arrangements, on-wafer testing and circular beam shapes.
Small area oxide-confined VCSELs are known to emit Gauss modes. Higher output powers can be achieved by larger active areas, but the emission changes to distributions best described by Fourier modes. The near field of the laser beam fills the complete pumped active area or emission area of the laser, which is e.g. determined by the shape of the oxide-aperture, by the shape of the proton implantation, by the shape of the mesa or by the shape of the contact geometry of the laser diode. By appropriately setting these shapes it is thus possible to generate different shapes of intensity distribution in the near field of a large area VCSEL like for example square, circular, elliptical or flower-petal shapes.
For many laser applications, especially in material processing or medical applications, special intensity distributions are required in the working plane, e.g. top-hat circular or rectangular shapes, lines or ring structures. Some applications require homogenous line-shaped intensity profiles, in particular with a very good uniformity along the line direction. An example is the drying of ink in a professional printing machine with a laser line up to 1.5 m and only some mm thick. Beam homogenizers consisting of one or several lens arrays and at least one Fourier lens can be applied to shape the laser beam to the desired intensity distribution but have to be carefully aligned in the beam. Furthermore, due to the coherence of the laser beam unwanted artifacts can appear. C. Singh et al., “Simulation and optimization of the intensity profile of an optical transmitter for high-speed wireless local area networks” 17th International Conference of Optoelectronics., Fiber Optics and Photonics, Dec. 9-11, 2004, Cochin University of Science and Technology, Kerala, Paper LTW-P2, disclose a vertical cavity surface emitting laser array-based multi beam transmitter with an optimized intensity profile. Using small area VCSELs with a Gaussian intensity profile and a special matrix type diffractive element in front the array, the intensity distributions of the individual VCSELs in the working plane are partially superimposed to achieve a uniform intensity distribution in the working or receiver plane.
In the known laser devices, a special optics has to be used and carefully aligned to generate a desired intensity distribution in the working plane. Furthermore, this intensity distribution can not be switched to a different shape without replacing the complete optics in front of the laser. This requires tailored systems for each application of such a laser.